Amplifying system



Jan. 2, 1934 G. L. BEERS 1,942,234

AMPLIFYING SYSTEM Filed May 1. 1950 Source Oscillator INVENTOR Q George L,Beers.

o n o o 0 WW I ATTEJRNEY Patented Jan. 2, 1934 UNITED STATES PATENT AMPLIFYING SYSTEM George L. Beers, Merchantville, N. J., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application May 1, 1930. Serial No. 448,862

1 Claim.

August 13, 1927, and assigned to the Westinghouse Electric and Manufacturing Company, I have disclosed means for automatically maintaining substantially uniform volume-control in a radio-receiving circuit. All the species described therein relate to generic means for accomplishing the desired result, the particular method comprising impressing the variable grid potentials of any one of a number of tubes in the circuit upon the grid of a control tube and,

subsequently, causing a corresponding variation in the potential drop across a resistor in the plate circuit of the control tube to be impressed, in reverse phase, upon the grids of certain of the tubes, to affect the grid bias thereon in a desired manner.

In the preferred embodiment, the grid of the control tube is operated from the grid of the detector. This particular system works to advantage with a power detector tube of the type 224 or 227 in the circuit, as the grid swing on those tubes is sufficient to operate the control tube directly, tubes of the above types being powerful enough to produce an eflicient loud-speaker output with a single stage of audio amplification.

It is an object of this invention to provide an amplifying system having automatic volume control and being capable of operating with tubes of the common types.

A more specific object of my invention is to provide an amplifying system wherein a volume-control tube may be controlled by a weak signal.

Other objects of my invention will be pointed .out in the following description taken in conjunction with the drawing, the single figure of which illustrates my invention as embodied in a radio circuit of the superheterodyne type.

The system, as disclosed, comprises an antenna circuit 1, a radio-frequency amplifier 3, first detector stage 5, an intermediate-frequency amplifier '7, a second detector stage 9, two stages of quency amplifier 13, are illustrated as of the al-' ternating-current heater type, but it is apparent that tubes of other types may be employed.

The cathodes of the radio-frequency, the intermediate-frequency and the first-audio stages are connected to a point 19 on the voltage di= vider 17. v The input circuits, comprising the inductor 21 and capacity 23 and the inductor 25 and capacity 27 of the radio-frequency and intermediate-frequency stages, respectively, and the grid 29 of the first audio stage are similarly connected to another point 31 on the voltage divider. The portion of the divider between the points 19 and 31, therefore, provides a fixed grid bias on the grids 33, 35 and 29 of the tubes referred toabove.

In like manner, that portion of the voltage divider between the points 3'7 and 39 provides gridbiasing potential for the first and second detector stages, for it will be seen that connections from both points can be traced, by means of conductors 41 and 42, to the cathodes 43 and i5 andthe low potential sides 47 and 49, respectively, of the input circuits of both of said tubes. I

The second stage of audio-frequency amplification comprises a three-element tube, the midpoint 51 of the filament circuit being connected to the low potential end 52 of the voltage divider, through a resistor 55 which provides grid-bias potential on the grid 57 of the tube by means of the conductor 59 connecting the lower end of the input circuit 61 to the negative end of the aforementioned resistor 55. 7

Plate potential for the various tubes is also supplied from the voltage divider. The anodes 63, 65 and 67 of the radio-frequency, intermediate-frequency and first audio stages are connected, through their respective output circuits 69, 71 and '73, to the point 75 of the voltage divider. The anodes 77 and 79 of the first detector tube and the second audio are connected to points 81 and 83, respectively, on the voltage divider.

As regards the second detector tube, it is shown coupled to the first audio stage by means of the choke coil and the resistance coupling 85, the circuit being traced from the anode 87, through the choke coil and the resistance element, to the point 89 on the voltage divider, the cathode 91 of the control tube making connection to this circuit at the high-potential end 92 ofthe resistor element 85.

To create a bias potential on the grid of the control tube, a connection is made fromthe grid 93 to a point 95 near the negative end of the potential source. This contact is adapted to be OFFICET V shifted, whereby it is possible to alter the volume level of the circuits to any desired value.

A resistor 97 in the common lead from the voltage divider at point 31 to the grid circuits 5 of the RF and IF stages is electrically connected to the plate 99 of the control tube. It will be noted that this resistor comprises theplate circuit of the control tube, as well as constituting a portionof the grid circuits of the RF and IF stages. tial drop across said resistor will react upon the grids 33 and 35 of the tubes in the above circuits.

The resistance of resistor 97 should be'several' times as great as that of resistor 85, since, otherwise, the plate current of the control tube flowing through resistor 85 would nullify the effect crease in strength, the current in the plate cir- -cuit of the second detector will tend to increase, causing a'tendency of the voltage drop across the coupling resistor 85 to become greater. This, in turn, will vary the grid bias of the control tube to make it less negative, with a resultant inr creaseof current in the plate circuit. This incr'e'asein current in the plate circuit of the control tube results in an increase in potential across the resistor 97 which, located as it is, in the grid circuits of the radio-frequency and inte rmediate-frequency amplifiers, will increase the negative bias in the grids of those tubes, thereby forestalling the tendency of the incoming signal being amplified above the volume level for which it was set.

5 Should the signal strength decrease, the effects Therefore, any variation in the potenon the system will be the reverse of what they are when the signal strength increases. The energy factor of the circuits will be increased to compensate for the deficiency in signal energy and, in this manner, maintain a substantially uniform volume level in the output of the system.

The effect on the input circuits or" the amplifiers, therefore, may be considered as being equivalent, but in reverse phase relationship, to the apparent changes in the output circuit of the amplifier associated with the control tube.

By connecting the input electrodes of the control tubes across the resistance coupling of the detector'tube, the control tube is adapted to be actuated by incoming weak signals, as well as by the strong signals, for the amplified potentials across the coupling are sufficiently large to work the control tube.

Transformer coupling might be used, in lieu of the inductive and resistance coupling illustrated, with equally efficient results. The inductance might, likewise, be eliminated andv only the resistance coupling used.

Therefore, while I have described my inven- 100 tion in great detail, I do not desire-to belimitedq to such details except insofar asis necessitated-r by the prior art and by thespirit of theappended' claim. 7

I claimas my invention: 5

In an amplifying system,=an amplifier and a; detector device each having -.an input and.-output circuit, and means for controlling thevol-. uine level of said system, said-.means compris ing an electric discharge device having aninput 1m and. an output circuit, said input circuit include ing a'cathode circuit, an impedance common to said cathode circuit and the output circuit-0L tioned impedance.

GEORGE L. BEERSz' 

